Remove flag to toggle CPU fusion in the presence of parallelism (#63514)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/63514
Test Plan: Imported from OSS
Reviewed By: navahgar
Differential Revision: D30417127
Pulled By: bertmaher
fbshipit-source-id: b77d7c68364f2af73570740540f3b1152313016e
